This application claims the benefit of a Japanese Patent Application No. 2002-007815 filed Jan. 16, 2002, in the Japanese Patent Office, the disclosure of which is hereby incorporated by reference.
1. Field of the Invention
The present invention generally relates to optical modules, and more particularly to an optical module which is made up of a semiconductor package and a metal casing, where the semiconductor package is provided with a semiconductor optical element and a metal base which is connected to the metal casing while maintaining an insulated state with respect to the metal casing.
2. Description of the Related Art
FIGS. 1A through 1C are diagrams for explaining an example of a semiconductor package. FIG. 1A shows a side view of a semiconductor package 1, FIG. 1B shows a plan view of the semiconductor package 1, and FIG. 1C shows a rear view of the semiconductor package 1. The semiconductor package 1 has a well known internal structure, and a description and illustration thereof will be omitted.
The semiconductor package 1 has a vacuum structure inside, and an optical element is mounted inside the semiconductor package 1 so that the optical element can optically couple to an optical fiber 2 which extends outside from a tip end of the semiconductor package 1. In order to achieve the vacuum structure and to maintain a sufficient mechanical strength, a circular base 3 is made of a metal. A cover 4 covers the tip end periphery of the semiconductor package 1. This cover is made of a synthetic resin, and has a generally cone shape towards the optical fiber 2.
A flange 6 having holes 5 used for mounting is provided on the base 3. For example, this flange is formed by removing top and bottom portions of a circular plate. As shown in FIG. 1C, four terminals 7-1 through 7-4 extend outwardly from the flange 6. The terminal 7-1 directly penetrates the metal portion of the base 3. The other terminals 7-2 through 7-4 are electrically insulated with respect to the base 3. Accordingly, the terminal 7-1 also functions as a ground (GND) terminal which is electrically connected to the base 3.
As shown in FIG. 1C, the terminals 7-2 and 7-4 are connected to a connection pattern on a terminal plate 8 by soldering. The terminal plate 8 is formed by a printed circuit board. The terminals 7-2 and 7-4 are connected to corresponding terminals 9-1 and 9-2 on both sides of the terminal plate 8 via a wiring pattern on the terminal plate 8. The terminals 7-1 and 7-3 extend via a cutout in the terminal plate 8. As may be seen from FIGS. 1A and 1B, the terminals 7-1 and 7-3 and the terminals 9-1 and 9-2 of the terminal plate 8 are arranged linearly in a horizontal direction.
Conventionally, in the optical module for use in optical transmission at a high bit rate of 600 Mbps or higher, a power supply voltage of a driving integrated circuit (IC) for driving the optical element such as a laser diode is xe2x88x925 V. For this reason, the terminal 7-1 and the base 3 are electrically connected as shown in FIGS. 1A through 1C so as to connect an anode circuit terminal and the base 3.
When combining the semiconductor package 1 and a driving LSI using a negative power supply voltage, the semiconductor package 1 is mounted on the metal casing so that the cathode of the laser diode is connected to xe2x88x925 V, for example, and the anode of the laser diode is connected to the ground (GND).
Recently, the driving IC for driving the laser diode uses a CMOS structure when transmitting at a high bit rate, and it has become possible to drive the laser diode using a power supply voltage of +3 V, for example. Hence, the laser diode of the semiconductor package 1 shown in FIGS. 1A through 1C which is conventionally combined with the driving IC using the negative power supply voltage, needs to be combined with the driving IC using a positive power supply voltage. But according to the conventional mounting method, the entire metal casing of the optical module including the semiconductor package 1 will have the potential of the positive power supply voltage.
More particularly, the terminals are connected so that the positive power supply voltage of an anode circuit of the laser diode is connected to the ground (GND) terminal 7-1, a cathode circuit of the laser diode is connected to the terminal 7-2 (9-1), and a monitoring photodiode for controlling light emission of the laser diode is connected to the terminals 7-3 and 7-4 (9-2).
When mounting the optical module described above on an apparatus, the terminal 7-1 is connected to a ground circuit of the apparatus, which would in turn short-circuit the power supply. Accordingly, it is necessary to electrically insulate the optical module. It is conceivable to form the metal casing by an electrically insulative material such as a synthetic resin, but the resistance of the circuit against electromagnetic noise deteriorates if the casing is not made of a metal.
FIGS. 2A through 2C are diagrams for explaining the semiconductor package 1 mounted on a metal casing 11. FIG. 2A shows a side view in cross section of the semiconductor package 1 and the metal casing 11, FIG. 2B shows a plan view of the semiconductor package 1 and the metal casing 11, and FIG. 2C shows a front view of the semiconductor package 1 and the metal casing 11.
The metal casing 2 has a box shape which is formed by bending four sides of a plate member such as a steel plate. An L-shaped metal fitting 12 is provided inside on the bottom surface of the metal casing 11 by soldering, for example. Four mounting terminals 13 with stepped portions extend inwards by being bent from the bottom surface of the metal casing 11, and four mounting terminals 14 extend outwards by being bent from the bottom surface of the metal casing 11. A pair of engaging projections 15 is press-molded on each of the two sidewalls of the metal casing 11. The entire metal casing 11 is subjected to a suitable rust-proofing process, such as nickel plating, which permits soldering thereon.
The mounting terminals 13 fit into corresponding through holes formed in a conductor pattern formed on a printed circuit board 16. The printed circuit board 16 is positioned to a predetermined height from the bottom surface of the metal casing 11 by the stepped portions of the mounting terminals 13. The mounting terminals 13 are soldered onto the conductor pattern in the state where the printed circuit board 16 is positioned. A plurality of lead terminals 17 are arranged in parallel on both sides of the printed circuit board 16, and these lead terminals 17 extend outside via cutouts formed in the bottom surface of the metal casing 11. Various circuit parts and circuit patterns are provided on the printed circuit board 16, but the illustration thereof is omitted in FIGS. 2A through 2C so as to simplify the drawing.
The flange 6 of the semiconductor package 1 connects to a vertical surface of the metal fitting 12 via an insulator plate 18 which is made of an electrically insulative material such as a synthetic resin. Screws 21 are inserted through the holes 5 via an insulator bush 19 made of a synthetic resin, from the front side of the flange 6, and are screwed into screw holes in the metal fitting 12, so that the flange 6 is fixed to the metal fitting 12. Accordingly, the flange 6 of the base 3 of the semiconductor package 1 is mounted with respect to the metal casing 11 in a state making no electrical contact to the metal casing 11. The tip end of the semiconductor package 1 projects outside the metal casing 11 towards the front side via a cutout 22 which is formed at the front side of the metal casing 11.
FIGS. 3A through 3C are diagrams for explaining a state where a metal cover is mounted on the structure shown in FIGS. 2A through 2C. FIG. 3A shows a side view of the structure, and FIG. 3B shows a plan view of the structure, and FIG. 3C shows a front view of FIG. 3A. The structure is shown with a metal cover 23 mounted on the metal casing 11 in FIGS. 3B and 3C.
The metal cover 23 has a box shape which is formed by bending four sides of a plate member such as a steel plate, similarly to the metal casing 11. A cutout 24 for permitting the semiconductor package 1 to project towards the front side, and rectangular holes 25 for receiving the engaging projections 15 on the sidewalls of the metal casing 11 are formed in the metal cover 23. The metal cover 23 is subjected to a suitable rust-proofing process.
The metal cover 23 has an internal surface shape which suitably matches an outer surface shape of the metal casing 11 when the metal cover 23 is fitted on the metal casing 11. Hence, when the metal cover 23 is slid in a direction indicated by an arrow in FIG. 3A and fitted on the metal casing 11, the metal cover 23 connects to the metal casing 11 as shown in FIGS. 3B and 3C. When the metal cover 23 is connected to the metal casing 11, all of the engaging projections 15 of the metal casing 11 engage the corresponding rectangular holes 25 in the metal cover 23, so as to positively hold the metal cover 23 and the metal casing 11 together. In this connected state, the tip end of the semiconductor package 1 projects towards the front side of the metal cover 23 via the cutout 24. The metal cover 23 can be removed from the metal casing 11 by outwardly spreading the sidewalls of the metal cover 23 and pulling the metal cover 23 with respect to the metal casing 11.
When mounting the optical module 26 on the printed circuit board or the like of the apparatus, the mounting terminals 14 of the metal casing 11 and the lead terminals 17 of the printed circuit board 16 are inserted into corresponding through holes in the printed circuit board of the apparatus. The terminals 14 and 17 are then soldered to wiring patterns on the printed circuit board of the apparatus.
As described above in conjunction with FIGS. 2A through 2C, the metal casing 11 and the base 3 of the semiconductor package 1 must be electrically insulated. For this reason, the insulator plate 18 and the insulator bush 19 are inserted between the metal fitting 12 and the flange 6 of the semiconductor package 1 when fixing the semiconductor package 1 to the metal casing 11 by the screws 21. However, since the parts are small and complex in structure, there was a problem in that it requires a troublesome and time-consuming operation to assemble such parts.
Accordingly, it is a general object of the present invention to provide a novel and useful optical module in which the problems described above are eliminated.
Another and more specific object of the present invention is to provide an optical module which can be assembled quickly by a relatively simple assembling operation.
Still another object of the present invention is to provide an optical module comprising a semiconductor package, a holder holding the semiconductor package, and a metal casing having a bottom surface, first and second confronting sidewalls, and third and fourth confronting sidewalls, where the first sidewall has a pair of parallel edges defining a cutout extending to the bottom surface, the holder is accommodated within the metal casing on the bottom surface in a state where the metal casing is positioned by the pair of parallel edges, the third and fourth sidewalls and the bottom surface, so that the semiconductor package extends outside the metal casing via the cutout. According to the optical module of the present invention, the optical module can be assembled quickly by a relatively simple assembling operation, without requiring special equipments or tools.
A further object of the present invention is to provide an optical module comprising a semiconductor package having a metal base, a flange and a semiconductor light emitting element which outputs an optical signal, a holder holding a periphery of the metal base of the semiconductor package, and a metal casing having a bottom surface and four sidewalls to accommodate the holder together with the semiconductor package, where one of the sidewalls has a pair of parallel edges defining a cutout extending to the bottom surface, the holder is made up of a pair of holder halves sandwiching the semiconductor package, each of the holder halves has a recess which positions the flange of the semiconductor package, a groove which receives the pair of parallel edges of the metal casing, and engaging portions which engage corresponding engaging portions of the other holder half when the pair of holder halves connect to form the holder, and the holder is electrically insulative at least at portions making contact with the metal base of the semiconductor package. According to the optical module of the present invention, the optical module can be assembled quickly by a relatively simple assembling operation, without requiring special equipments or tools.
Another object of the present invention is to provide an optical module comprising a semiconductor package having a metal base, a flange and a semiconductor light emitting element which outputs an optical signal, a holder holding a periphery of the metal base of the semiconductor package, and a metal casing having a bottom surface and four sidewalls to accommodate the holder together with the semiconductor package, where one of the sidewalls has a pair of parallel edges defining a cutout extending to the bottom surface, the holder is made up of a pair of holder halves made of a synthetic resin and sandwiching the semiconductor package, and each of the holder halves has a recess which positions the flange of the semiconductor package, a groove which receives the pair of parallel edges of the metal casing, and engaging portions which engage corresponding engaging portions of the other holder half when the pair of holder halves connect to form the holder. According to the optical module of the present invention, the optical module can be assembled quickly by a relatively simple assembling operation, without requiring special equipments or tools.
Still another object of the present invention is to provide an optical module comprising a semiconductor package having a metal base, a flange and a semiconductor light emitting element which outputs an optical signal, a holder holding a periphery of the metal base of the semiconductor package, and a metal casing having a bottom surface and four sidewalls to accommodate the holder together with the semiconductor package, where one of the sidewalls having a pair of parallel edges defining a cutout extending to the bottom surface, the holder is made up of a pair of holder halves sandwiching the semiconductor package, each of the holder halves has a recess which positions the flange of the semiconductor package, a groove which receives the pair of parallel edges of the metal casing, and engaging portions which engage corresponding engaging portions of the other holder half when the pair of holder halves connect to form the holder, and the holder is electrically insulative at least at portions making contact with metal portions of the semiconductor package and including the flange of the semiconductor package. According to the optical module of the present invention, the optical module can be assembled quickly by a relatively simple assembling operation, without requiring special equipments or tools.
Other objects and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings.